Spokesman Rupert Colville said his office was concerned by the level of violence tied to ongoing protests in Kiev.
"We are also calling for an investigation into reports of kidnappings and torture," he said in a statement Friday.
Protests erupted in Ukraine, a former Soviet republic, in November when the government backed off efforts to sign an association agreement with the European Union, saying it needed to protect its economic ties with Russia. Demonstrations turned violent in January when the government passed laws restricting protests, a measure that's since been repealed.
Ukrainian activist Dmytro Bulatov was quoted by the BBC as saying he was "crucified" after being kidnapped by abductors he said spoke with Russian accents.
Ukrainian authorities were criticized for using force to quiet protests, though authorities said they were protecting state institutions from violent demonstrators.
Colville said Friday he welcomed the start of dialogue between President Viktor Yanukovych and members of the opposition.
"We call for this dialogue to be sustainable, inclusive and grounded on the full respect of international human rights treaties," he said.